News analysis: Does the 5:2 fast diet work?

Note – this article, originally written in January 2013, was updated in May 2013.

The 5:2 diet is an increasingly popular diet plan with a flurry of newspaper articles and books being published on it in the run up to Christmas 2012 and in January 2013.

The diet first reached the mainstream via a BBC Horizon documentary called Eat, Fast and Live Longer, broadcast in August 2012.

The 5:2 diet is based on a principle known as intermittent fasting (IF) – where you eat normally at certain times and then fast during other times.

The 5:2 diet is relatively straightforward – you eat normally five days a week, and fast on the other two days.

What does a daily 600-calorie diet look like?

A 600-calorie diet could consist of a slice of ham and two scrambled eggs for breakfast and then some grilled fish and vegetables for your evening meal. And of course nothing but water, black coffee and/or green tea to drink.

Champions of the 5:2 diet claim that other than helping people lose weight, 5:2 diet can bring other significant health benefits, including:

increased lifespan

improved cognitive function and protection against conditions such as dementia and Alzheimer’s disease

protection from disease

However the body of evidence about 5:2 diet and intermittent fasting is limited when compared to other types of weight loss techniques.

What we don’t know about intermittent fasting

Despite its increasing popularity, there is a great deal of uncertainty about IF with significant gaps in the evidence.

For example, it is unclear:

what pattern of IF is the most effective in improving health outcomes – 5:2, alternative day fasting, or something else entirely different

what is the optimal calorie consumption during the fasting days – the 5:2 diet recommends 500 calories for women and 600 for men, but these recommendations seem arbitrary without clear evidence to support them

how sustainable is IF in the long-term – would most people be willing to stick with the plan for the rest of their lives?

Are there any side effects from intermittent fasting?

Little is known about possible side effects as no systematic attempt has been made to study this issue. Anecdotal reports of effects include:

difficulties sleeping

bad breath (a known problem with low carbohydrate diets)

irritability

anxiety

dehydration

daytime sleepiness

However, more research would be needed to confirm these side effects and their severity.

If you are fasting, you may want to think about how fasting will impact on your life during your fasting days. You are likely to be very hungry and have less energy and this could affect your ability to function (such as at work), in particular it may affect your ability to exercise which is an important part of maintaining a healthy weight.

Also, IF may not be suitable for pregnant women and people with specific health conditions, such as diabetes, or a history of eating disorders.

Because it is a fairly radical approach to weight loss, if you are considering trying IF for yourself, it is wise to speak to your GP first to see if it is safe to do so.

Evidence about the 5:2 diet

But since this article was originally written in January 2013 we have been alerted to research, led by Dr Michelle Harvie, which did look at the 5:2 model.

In one study carried out in 2010 the researchers did find that women placed on a 5:2 diet achieved similar levels of weight loss as women placed on a calorie-controlled diet.

They also experienced reductions in a number of biological indicators (biomarkers) that suggest a reduction in the risk of developing chronic diseases such as type 2 diabetes.

A further study in 2012 suggested that the 5:2 model may help lower the risk of certain obesity-related cancers, such as breast cancer.

The increasing popularity of the 5:2 diet should lead to further research of this kind.

Evidence about other forms of IF

There is some degree of evidence about the potential benefits of other forms of IF – albeit with some limitations.

It should be stressed that our assessment of the evidence was confined to entering a number of keywords into Google Scholar and then looking at a small number of studies which we felt would be useful to explore further.

We did not carry out a systematic review (though arguably, it would be useful for researchers to do so). So the information provided below should be taken in the spirit of us trying to provide an introduction to some of the evidence and science of IF – not an exhaustive "last word" on the topic.

Is there any evidence that intermittent fasting aids weight loss?

One of the most recent pieces of research on intermittent fasting is a 2012 study (PDF, 291kb) that recruited 30 obese women known to have pre-existing risk factors for heart disease.

After an initial two-week period they were then given a combination diet of low-calorie liquid meals for six days of a week (similar to Slim Fast diet products) and then asked to fast for one day a week (comsuming no more than 120 calories).

After eight weeks, on average, the women lost around 4kg (8.8lb) in weight and around 6cm (2.3 inches) off their waist circumference.

However, there are a number of limitations to consider when looking at this as evidence that it might be a generally beneficial thing to do for most ordinary people, including that:

These women may have had increased motivation to stick with the diet because they knew their weight would be monitored (this is a psychological effect that slimming clubs make use of).

The women had been told that they were at risk of heart disease. It is uncertain how well most of us would cope with such an extreme diet.

The follow-up period was short – just two months. It is not clear whether this diet would be sustainable in the long term or whether it could cause any side effects.

30 people is quite a small sample size. A much larger sample – including men – is required to see if intermittent fasting would be effective in most overweight or obese people.

Is there any evidence intermittent fasting increases lifespan?

There is quite a wide range of work on the effects of IF on combating the effects of ageing, but almost all of these studies involved either rats, mice or monkeys. One big problem with studies in animals – particularly rodents – is that they are only expected to live for a few years. While this makes them ideal subjects for longevity studies, carrying out similar, more useful experiments in humans, requires decades-long research to gain credible results.

In an unsystematic look at the evidence, we find only one study involving humans: a 2006 review (PDF, 65kb) of an experiment actually carried out in 1957 in Spain.

In this 1957 study, 120 residents of an old people’s home were split into two groups (it is unclear from the study whether this was done at random). The first group (the control group) ate a normal diet. The second group (the IF group) ate a normal diet one day and then a restricted diet (estimated to be around 900 calories) the next.

After three years there were 13 deaths in the control group and only six deaths in the IF group.

This study is again limited by the small sample size meaning that the differences in death are more likely to be the results of a statistical fluke. Also, many experts would feel uneasy about issuing dietary guidelines based on a study over half a century old with unclear methods. It is unlikely that this experiment could be repeated today – denying food to elderly people in residential care is unlikely to be looked at kindly by an ethics committee.

Is there any evidence intermittent fasting prevents cognitive decline?

It seems that all of the studies on the supposed protective effects of IF against conditions that can cause a decline in cognitive function (such as dementia or Alzheimer’s disease) involve animals.

For example, a 2006 study (PDF, 843kb) involved mice that had been genetically engineered to develop changes in brain tissue similar to those seen in people with Alzheimer’s disease.

Mice on an IF diet appeared to experience a slower rate of cognitive decline than mice on a normal diet (cognitive function was assessed using a water maze test).

While the results of these animals tests are certainly intriguing, animal studies have inherent limitations. We can never be sure that the results will be applicable in humans.

Is there any evidence that intermittent fasting prevent diseases?

Much of the published research into the potential preventative effects of IF involve measuring biological markers associated with chronic disease, such as insulin-like growth factor-I (IGF-I) – known to be associated with cancer.

Using these kinds of biological surrogates is a legitimate way to carry out research, but they do not guarantee successful real-world outcomes.

For example, some medications that were found to lower blood pressure readings taken in laboratory conditions failed to prevent strokes once they had been introduced for use in the healthcare of patients in the world.

A 2007 clinical review (PDF, 119kb) looking at the effects of IF in humans in terms of real-world health outcomes concluded that IF (specifically, alternative day fasting) may have a protective effect against heart disease, type 2 diabetes and cancer. However, it concluded "more research is required to establish definitively the consequences of ADF (alternative day fasting)".

Conclusion

Compared to other types of weight loss programmes the evidence base of the safety and effectiveness of the 5:2 diet is limited.

If you are considering it then you should first talk to your GP to see if it is suitable for you. Not everyone can safely fast.

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Comments

The 63 comments about ‘News analysis: Does the 5:2 fast diet work? - Health News - NHS Choices’ posted are personal views. Any information they give has not been checked and may not be accurate.

amiewall said on 13 January 2015

I agree with your comment that personal anecdotes shouldn't trump scientific evidence, however its is incorrect to claim 'The article was a fair assessment of the intervention being studied, based on the available evidence regarding that intervention.'. As the author says 'We did not carry out a systematic review ... So the information provided below should be taken in the spirit of us trying to provide an introduction to some of the evidence and science of IF'. This article could be described as broadly negative and I don't believe it gives an accurate overview of IF. For example the author states multiple times that animal studies would need to be repeated on human subjects to confirm the findings of these studies. This is true, however for example to confirm the effect of IF on cognitive decline in human Alzheimer's sufferers (as I feel the author is suggesting), a large sample size of sufferers would have to be used and given no treatment other than IF. Indeed 50% would have to be given a placebo, meaning this group would have no treatment what so ever. This clearly could never realistically happen. I personally think this article should be re-written to give a non-biased overview of whether the 5:2 diet/IF works.

David N Andrews said on 29 June 2014

It pains me to see people trying to insist on personal anecdote trumping scientific evidence: it doesn't, so - no matter how hard you try to claim that it does, it's all hot air.

The article was a fair assessment of the intervention being studied, based on the available evidence regarding that intervention. There are many reasons why, interesting as they are, personal anecdotes are not really considerable as evidence. The main one is the lack of control over the circumstances surrounding them.

Whilst personal experience/anecdote is, on its own, very poor as evidence goes, there is a way to improve its usefulness in making decisions about health and other important choices (e. g., education, therapy amd so on). This involves data collection, implementing and removing the intervention, having other people observe and recorded data and so on; so most people will not do this. It seems they are not interested in putting some 'substance' to their claims. But, without that 'substance', anecdotal claims have no real evidentiary value.

There is way too much Dunning-Kruger in the comments below mine. That is the result of successive governments dumbing down the science content of the school curriculum: scientific illiteracy.

If this comment angers anyone... then I've done my job. Because, if someone can be bothered to get angry about this comment and yet not be bothered to do something to substantiate their personal anecdotes/experiences, then that definitely highlights a problem of investigative laziness/lackadaisicality. That remains the angered reader's problem to sort out, not mine.

LurcherLady said on 27 June 2014

The authors seem to ignore the fact that ordinary dieting doesn't work. My experience is that trying to diet on 1500 Cals a day (the traditional way) means that I'm hungry every day, I'm thinking about food all the time and I give up because it's all so miserable and depressing. I've been trying the 5:2 diet for 4 weeks now and have lost 2kg. I'm hungry 2 days a week, but no hungrier than when I tried a normal diet, and I can get through the "fast" days by thinking about eating normally the following day. There's also no mention in the article of the idea that normal dieting affects your metabolism, your body adjusting to the lower calorie intake so that when you start eating normally (2000 Cals a day), you put weight on. That sort of yo-yo dieting is supposed not to happen with the 5:2 diet as your body doesn't get used to the lower calorie intake.If this is true, then when I get to my target weight I should be able to maintain it. The authors suggest that you might not have enough energy to work or exercise on the fast days. This hasnt't happened to me - I'm retired, but on a typical fast day I've walked the dog for 2 hours, painted 3 large trellis panels, mown the lawn and done some gardening. Different people need to use different methods. If traditional dieting doesn't work for you, this seems worth trying. I've been fasting today. It's 11pm and I feel fine - I'm looking forward to having breakfast tomorrow.

helenlondon said on 11 June 2014

I think the authors of this article fail to understand the psychological effects of the 5:2 diet, which really assist with readjusting portion control on the non-fasting days. After being on the diet for five weeks and losing 11lbs. I now feel in control of my eating again. I am in my 50s, was overweight and had despaired of ever losing weight again. The most important thing is that after nearly six weeks, I don't think I will have any difficulty continuing with this diet. I can now recognise when I am full again and stop eating. Many people find they simply fail after a few weeks of being on a daily diet where they are permanently needing to think about and ration their food. The authors need to consider the efficacy (in terms of numbers of successful dieters) when weighing up the overall health benefits of the plan.

J_Alfred said on 23 May 2014

"While the results of these animals tests are certainly intriguing, animal studies have inherent limitations. We can never be sure that the results will be applicable in humans."

Why can we never be sure? Never seems quite a bold word for what is meant to be a science based analysis. I think what you mean is we cannot be sure the results will be applicable, based on our current understanding and technological limits. That doesn't however mean 'never.' It is not that far fetched to imagine a future where we are able to better model what occurs in a human body (e.g. in computer simulation or possibly in vitro) and so we could be sure if the result are or are not applicable in humans.

People probably thought we would 'never' be able to see into a living human body either. And then we got x-rays, MRI scans...

Dummerchen said on 28 February 2014

"One of the most recent pieces of research on intermittent fasting is a 2012 study (PDF, 291kb) that recruited 30 obese women known to have pre-existing risk factors for heart disease."

There were 54 study subjects. The diet was restricted to 800 - 1000 kcal 6 days a week for 10 weeks and to 120 kcal on the 7th day. This regime has nothing to do with intermittent fasting, whether 5:2 or ADF or 16:8. This is shoddy craftsmanship on your side.

Although scientific evidence for or against IF might still be limited, real life experience is plentiful. If fasting was dangerous NHS hospitals would be devoid of staff as there is often not enough time to have a break and a meal. Yet all these people continue to life and work.

You might not like IF because it goes against everything drummed into our heads for decades but there is no need to make your dislike so obvious.

idr said on 24 February 2014

At age 70+, this the first eating plan that has EVER worked for me and not for a want of trying. I'm one of those unfortunates who despite a healthy diet and plenty of exercise still hover around the edge of obesity. If I wasn't so careful I would weigh 25 stone. I believe it to be the result of overfeeding as a child, not junk but, good healthy homecooked food in far-too-generous portions.

I have been following 5:2 for just over a year and have lost a mere 7 kilos (15.4 lbs). I'm aiming for 10 or even 15 more. Despite the slow weight loss, my BP is now on the low side of normal, cholesterol 4.8 and no sign of high blood glucose, despite having had 2 diabetic parents. Also previously uncomfortably tight clothes now fit perfectly while others have found their way to the charity shop.

Lewis Clifford said on 20 February 2014

I can only speak from a personal perspective. I have been on 5:2 Diet and I have lost 10 lbs on 5 weeks. I'm not a big person, but was conscious that being in my mid Forties my weight had been going up the older I get.But, anecdotally I do feel energised, and generally more healthy as a result.

rfbh said on 05 February 2014

I am 65 and put on weight after I was 50. I went to the gym 5 times a week for an hour for 7 years and although I became very fit, I didn't lose a pound. I have been doing the 5:2 diet for 9 months, have lost over 2 stone and am now well within my healthy weight range.. We are always being scolded about how obesity is costing the country millions so how about the government funding some research into the fasting diet since it seems to have such good results? This article was pathetic. Flabby advice like exercise regularly and eat healthily has just resulted in an obesity epidemic. I find the 5:2 diet easy to follow and effective. My blood pressure and blood sugar levels are now well within normal limits whereas they were edging up before. I look and feel much better and still go to the gym regularly. What''s the problem?

richard_no1 said on 14 January 2014

My wife and I have been five and two-ing since the Horizon programme. I lost over two stone in 4 months and have maintained that for a year. My wife, who is not significantly overweight, lost over a stone in the same period but has put a bit back on since (cake and bread baking and consuming!) We're in our 60s and I've been a type 2 diabetic for 16 years. Since I started 5:2 fasting, my blood glucose is now well controlled (HbA1c 42 or 6% in old money) and the doctor has significantly reduced my medication.

I'm writing this late-afternoon on a fasting day, having had porridge with water this morning (95 cals) and nothing since. I've cycled for 45 minutes and done office work and feel on top form - alert, not tired and not very hungry. My blood glucose is 5.2 - so no hypo! I'm looking forward to a M&S Fuller Longer meal of cod mornay with veg this evening (310 cals) followed by some fruit.

I think the information above is fine - there clearly isn't much science behind this and my experience is purely anecdotal but 5:2 has worked for us and we plan to continue indefinitely

MrPudMan said on 13 January 2014

The above article contradicts with another nhs.uk article:

http://www.nhs.uk/Livewell/Healthyramadan/Pages/fastingandhealth.aspx

So many people have benefited from 5:2 (myself included) and I had never had never suffered from the side effect of: difficulties sleeping, bad breath, irritability, anxiety, dehydration nor daytime sleepiness.

Tri With Me said on 09 January 2014

I have been on the 5 2 diet for 15 months. My body fat has dropped from 22% to 10%. The first couple of weeks were the hardest but then for me it all settled down and became quite an easy process. After a weekend of over eating I looked forward to a Monday low cal day. I posted some more info on TriWithMe herehttp://www.triwithme.org/blog/5-2-diet

DHDW said on 08 January 2014

I think your article is negative and unhelpful. It puts people off trying a really effective method of losing weight, while making bland, ineffective suggestions at the end.

My partner and I have followed the 5:2 diet since Aug 2012. She's 65, I'm 66. We're both fairly active, but were somewhat overweight. She's shed 18lbs and I've shed 27lbs. We find we can easily maintain that weight loss if we follow the diet most weeks. If we stop, we slowly gain pounds, but resuming the diet slowly takes them off again.

It's misleading to call diet days "fasting". You can still eat 500 or 600 calories. We find the easiest way to achieve this is to restrict ourselves to fruit and vegetables on those days, as you can then eat quite a lot without going over the limit. A typical day would be leek soup, grilled mushrooms and lots of fruit. We don't feel any great hunger pangs. The only difficulty I've noticed is I can feel cold that evening, so I tend to go to bed early. We sleep well, and, surprisingly, when we wake up we don't feel especially hungry. It's easy to under-eat one day, if you know you can eat what you like the following day! We typically diet Mondays and Thursdays.

I was impressed by the science in the original Horizon programme. We started the 5:2 diet for the health benefits rather than to lose weight as such. Losing weight, without any great difficulty, was a bonus.

I can't say whether the 5:2 diet has achieved any special health benefits for us. But we do feel younger and fitter. If nothing else, you feel much more active and energetic not having to carry around a considerable extra weight! My body feels more supple, and less liable to the back pain I used to get.

The accepted menus for 5:2 diet days seem to focus a lot on animal protein, and for that reason seem unbalanced and unappealing to me. If "five-a-day" fruit and veg is good in general, why abandon it on diet days?

Andrew Ford said on 03 January 2014

I have had great results from Intermittent Fasting. I am a 56-year old, type 2 diabetic (managed by drugs, diet and exercise). I have been fasting 3 days a week for 15 months, although sometimes I am not necessarily strict about it. I have lost over 20 pounds in that time, reducing my BMI from 26 to 22.5, and have no problems running a five mile run on a fasting day. I reduce my medication in the evening of a fasting day if I have exercised and my blood glucose is normal (for me) the following morning. In fact I have records of my morning blood glucose stretching back to diagnosis almost 10 years ago, and my diabetic control has been much better since I started intermittent fasting.

I love the simplicity of the diet - it is really more of a lifestyle. I feel it has reeducated my palette and I can distinguish now when I want to eat for reasons other than hunger (such as boredom usually or being thirsty). And hunger pangs are not that bad - they come and go during the day. If I have an urge for a calorific treat, I tell myself I can have it the next day, by which time often I don't actually want it.

Malcolm from Dorset said on 01 January 2014

I found the above article somewhat patronizing and negative. I have used 5:2 (two consecutive days) to lose 28lbs over 6 months. I also did the obvious things - more walking and moderation on non-fast days - and gave some thought to what I did eat. At first I thought about how I felt, and was prepared to break the diet if I felt unwell. I had hunger pangs - but they weren't that bad. I tried to keep busy until they had passed. They always did. Some nights I woke up very early. Some days I felt the cold more. But none of this was life threatening, and I was never more than one or two days away from "normal" food anyway. We're not talking about weeks of starvation. It is fair to say that some people shouldn't fast (at all, presumably), even a short term partial fast, but it would have been more helpful to identify the relevant circumstances. Most people could do this quite easily. It is also fair to point out that not all weight loss regimes suit all people. 5:2 worked for me, but I know people who didn't get on with it and succeeded with other methods. You need to find what suits you. I also know a LOT of people who have lost weight on 5:2, generally healthy "normal" people. It's worth a try, doesn't cost anything, can be planned around your work and social life, and can easily be dropped. So I would recommend it on that basis. I don't know if I will live longer, but I definitely wear smaller trousers and feel better. Of course, no diet will keep weight off afterwards. But that's a different subject.

grekophile said on 04 August 2013

I am a 71 year old male. I have followed the 5:2 diet since Christmas, as I was overweight, though physically active still playing a regular game of squash. My weight has reduced from 90kg to 79 kg, and my blood pressure is also reduced (150/90 down to 130/72). My waist size is just over 2" smaller, and I feel physically much fitter, I take active exercise on calorie restricted days, and feel mentally more alert when "fasting". Several of my friends are also on the regime, and all record similar results and benefits. I think the effects on weight and blood pressure are worthwhile- realistically, I can now bend down to do up my shoelaces without feeling breathless- a former problem. I think I have lost quite a lot of internal fat. As the book suggests, after a calorie restricted day, I eat normally the next day, and I tend to eat less meat and more fruit and vegetables, as these make the 600 calorie restriction easier to achieve. My experience is all positive so I would recommend friends to try IF provided they do not have medical problems that make it hazardous.

jennenny said on 04 July 2013

This is more a question than a comment. I started on the 5 2 diet about 5 weeks ago after seeing Michael Moseley's documentary as like him I am prediabetic and was hopeful it might help me improve my glucose metabolism. I am already on the slim side and have no wish to lose any weight and am wondering if anyone knows if it is believed there might be benefits with regard to glucose metabolism and other health issues in someone who has no need to lose a few kilos?I have already lost a couple of kilos but so far have seen no improvement in my FBG.Hoping someone out there might have an opinion on this.

martha16 said on 27 May 2013

If something sounds too good to be true then it normally is....as in the case of the 5:2 fasting diet, in my opinion. I have no axe to grind only pounds to lose. I would suggest this diet only works if you are prepared to fast and eat a low calorie diet on the non fast days and this is not what is mentioned in the all singing and dancing media interviews and write ups. I have been doing this for 5 months and weight loss has been slow and if I have a few days of overeating while continuing with the two days fasting the weight actually goes up. I find it galling being pursuaded in the media about this wonder diet with the author parading in a bikini have lost lots of weight...I believe it is not realistic and it preys on people desperate to lose a few pounds.

slimmerme said on 18 May 2013

Having, over the years tried Slimming World diet and Dr. Atkins which were fine but soon put on weight again and more, I started the 5:2 diet at the end of January - now May and have lost 20lbs and am delighted at the weight loss and how good I feel, but have someway to go still. When I told the Doctor about this diet he said, "Good - Keep it up". I have found that it is important to keep hydrated and drink plenty of water on diet days. I treat the Diet Days as a challenge and know I can eat normally the next few days. However, I have reach a bit of a plateau and have not lost anything for 2 weeks but will keep going and maybe be a little more portion control conscious on non diet-days. I will be having results of various blood tests this coming week, so I will see what they say! Finally, it is a diet that is relatively easy to sustain and hopefully when I have reached the weight I want to maintain I will go on to a 1 day regime.

jhall52 said on 19 April 2013

Apologies for the multiple posts, this is due to the character limit.Most of the arguments in this article are theoretical, with little to no supporting evidence as are NHS recommendations. Studies often used to show benefits of various diets such as the 'paleo' diet, regarding food composition in fact show correlations between health and irregular eating patterns. Mixed food meals and designation of regularity, such as three meals a day with mixtures of food types are socio-cultural inventions. Diet balance is in fact important over long periods to ensure maintenance of molecular and electrolyte balance and correct metabolic functioning in the body. There is no real evidence suggesting this has to occur daily, or at any meal, as the gut is remarkably well formed to take up required nutrients and can adapt during the normal cell cycles of the lumina to dietary changes incredibly well.Supposing arguments against research results without detailing the paper is an example of cherry-picking and much of this article almost borders on suggesting confirmation bias. Medical dieticians would do well to keep up with research as the rest of us have to, in order to retain credibility. It is tiring to see the same statements being pushed in the face of emerging and conflicting evidence.Finally, before I am accused myself of bias, I would like to add I have no plans to make a name for myself in dietetics or the weight loss world, I have no book to plug and do not plan on submitting any paper on this subject, nor do I work for any employer which has this on its agenda. Pretty much all of this information can be seen in any undergraduate physiology book, or accessible published literature.Lastly my personal advice for anyone seeking dietary advice: given the state of modern dietetics, you'd be much better off speaking to s cardiologist (which I am not).

jhall52 said on 19 April 2013

Now regarding the diet itself. Kumar & Clark, and virtually all clinical texts, state that there is a positive correlation between dietary energy restriction and longevity. There is also published evidence that very short term fasting, often leading to glycolytic states, but rarely ketosis, is not harmful to health in humans except in certain metabolic pathologies or medication use, and may even provide health benefits especially to the digestive and cardiorespiratory systems dueto decreased metabolic demand. There is also some, albeit restricted research that eating large meals increases risk factors of disease for up to 24 hours, particularly cardiovascular disease and events, such as MI and stroke. While the specific 5:2 diet pattern has scant controlled research there is a large body of clinical and anecdotal evidence demonstrating efficacy and safety. Several eating patternshave been and continue to be investigated, while the NHS sticks to unfounded advice. In fact we only know very little about human nutrition, such as high sodium intake should be avoided. The field of dietetics, especially in the UK, is a naive and unaccepting science, filled with half-truths and common knowledge. For instance it is not widely realised that carbohydrates are not actually an essential nutrient, nor is there evidence that vegetables are even needed in human diets, whilst animal derived foods and fruits contain nutrients essential to normal health.

jhall52 said on 19 April 2013

As a biologist, medical science researcher and post-graduate medical student, I feel obligated t add some corrections, both to the article and some comments. Firstly, regarding side-effects: anyone who has smelled ketones on the breath would never describe this as 'bad breath'. In fact bad breath is more of an issue in high carbohydrate and vegetable diets. There is also no evidence in the published literature of short term fasting in health and many morbidity states causing dehydration, except in extreme activities or climates.Moving on to NHS dietary recommendations: the '5-a-day' slogan is not based on any scientific research, nor are the quantity size recommendations. Modern cultivated fruits and vegetables would require much more than these quantities to provide adequate nutrition in the recommended macro-nutrient ratios. Neither are the recommended daily energy intakes accurate, except in the average sized sedentary adult in normal health. For the NHS to recommend dietary habits without scientific backing, whilst downplaying active research areas, or even dismissing them in spite of contradictory evidence demonstrates the inability of the NHS to respect scientific progress and evolving understanding.

forgetdieting said on 16 April 2013

We've lost a lot of weight doing something similar to the 5:2 diet but which we started well over a year before Dr Mosely's prog was aired. We did not fast either, yet lost all the weight. We recorded everything in a diary which we kept online in a blog. What we did was very similar to what doctors tend to recommend I suppose, that's eat a little less and exercise a little more (we did a little walking). We just came up with a slightly different concept, which allowed us to steadily lose weight and keep the weight off. I'm sure the nhs would be interested, but not sure who to contact about it. Fasting is not something we could have done really, as we like eating.

Target for the first six weeks: 4 pounds per week (total of 24 pounds).

During this time, I will note down how the diet affects my sleeping, bad breath, irritability, anxiety, dehydration, and daytime sleepiness (more than usual, that is).

I shall attempt to hold to my regular weekly exercise pattern: one Zumba class, one gentle circuit class (for over 50s), a walk of at least one mile per day – and note whether the diet adversely affects my energy levels.

Target for the first six weeks: 4 pounds per week (total of 24 pounds).

During this time, I will note down how the diet affects my sleeping, bad breath, irritability, anxiety, dehydration, and daytime sleepiness (more than usual, that is).

I shall attempt to hold to my regular weekly exercise pattern: one Zumba class, one gentle circuit class (for over 50s), a walk of at least one mile per day – and note whether the diet adversely affects my energy levels.

Brian Walpole said on 11 March 2013

One of the most convincing theories about intermittent fasting suggests that depriving the body of food for short phases gives it a respite from the rigours of digestion, cleanses the body of accumulated toxins and has a rejuvenating effect on all the systems. Another logical argument in favour of IF is that our metabolic rate is directly proportional to the number of times we eat. So the more frequently you eat, the hungrier you are likely to get and this seems like an open invitation for overeating. Eating fewer meals translates into a lower calorific intake and a feeling of satiety due to reduced frequency of hunger. However Intermittent fasting could be used as an effective way to control weight only when it is practiced occasionally and with the right attitude. It should not be used to compensate for an unhealthy diet due to poor food choices or become a pretext to justify an eating disorder. It will also prove absolutely ineffective if you binge more than you should during your “eating window”.

User752392 said on 01 March 2013

It's interesting that the author(s) of this article make a lot of noise about the lack of scientific evidence for the 5:2 diet and yet go on to repeat the recommendation to eat 5 portions of fruit and veg a day. Where is the scientific evidence for this??? It's a number made up by the farming industry to sell more fruit and veg.

aby385 said on 10 February 2013

what is the fuss all about i really don't know cos as a Muslim we have to fast for a whole month once a year every year and no one has died from fasting and you also lose weight depending on what you eat when you open the fast. even children of certain age have to fast also teaches self discipline

SteveGrubb said on 06 February 2013

What a useless article, it would have been better to just say 'we don't know' and leave it at that. It is full of if's and maybe's, nothing is factual. True that everyone knows that the right answer is a sensible diet and exercise - but even so we have a country with a growing obesity problem so clearly this isn't an easy regime for so many people.

Why don't you conduct some research and come back when you have something to say on the matter? Until then please don't bother.

Tartangirl said on 06 February 2013

No one seems to have said much about water but surely to avoid dehydration on fast days you need to consume plenty of water. I read somewhere that sipping steadily throughout the day keeps you hydrated, keeps any hunger pangs you may have at bay, and surely has gotta be good for your skin, brain energy levels and overall health too. I'm certainly going to give the 5:2 a try - it may not be a regular three meals a day (which we're told is best) but how can it possibly be any worse for me than some of the days when I grab junk food on the run, skip meals and live on coffee - which i'm sure many of us do.

Ingheanrae said on 05 February 2013

This nonsense is typical of the advice coming com the NHS right now. Anything it doesn't understand is dismissed. As others have pointed out there are some quality trials being conducted based on promising initial results of studies with human subjects. A search on Google Scholar is elementary stuff. Clearly the 'tried and tested' methods of weight loss do not work as many overweight people struggle to maintain weight loss or even lose weight. I have ME - a conditions with a clear physiological basis but which has unknown aetiology. I and other sufferers constantly have to deal with the so-called evidence based nonsense spouted by 'experts'. It usually has a political bias and tends to disregard the views of real experts and their patients. the evidence they cite is often of dubious quality e.g the PACE trial, has been discredited by knowledgable experts in the field yet is promoted by the NHS because there is a powerful cadre of medical practitioners in league with politicians and private health insurance companies who have vested interests in finding psychological interpretations of chronic morbidity state to avoid spending money on serious research.

crabsallover said on 03 February 2013

the article said "The diet first reached the mainstream via a BBC Horizon documentary called Eat, Fast and Live Longer, broadcast in August 2012."

The book 'The Fast Diet - The simple secret of intermittent fasting: Lose weight, stay healthy, live longer" by Michael Mosely and Mimi Spencer was published early in January 2013 by Short Books.

Does the evidence included in this book advance our understanding about whether Intermittent Fasting is likely to; increase our life-span, improve cognitive function, protect against dementia and Alzheimer's disease and other diseases?

Theo99 said on 02 February 2013

I follow the IF since September of 2012. My weight was195lbs when I started. Currently my weight stands at 174lbs. My approach is to fast on Monday, Wednesday, and Friday. I feast the rest of the week. I did blood testing both before I started the fasting approach and most recently two weeks ago.

My cholesterol went from 226 to 182 and the triglycerides from 160 (borderline diabetic) to 60.

So I found little that was useful and convincing in the article. Yes, there things we don't know about IF but I feel great and my blood chemistry looks picture perfect according to my doctor. So unless my hair starts falling out, I will continue with this eating approach,

Boggey79 said on 31 January 2013

My GP told me not to do 5:2 as it lacked evidence and it's dangerous to fast. For one it's not truly fasting, rather calorie restriction and secondly why did the NHS invest millions into Homoeopathy? She refused even to refer me for a cholesterol check on the basis I'm not in a risk category. I found her attitude to be incredibly belligerent. I guess the NHS would rather I came back when I'm in need of Statins, rather than take pre-emptive steps.

Big-H said on 31 January 2013

Interesting but this was a non-scientific article and does nothing to convince me of the scientific validity of this website in general.Dieting is a very difficult process; all but this scheme require absolute dedication and adherence, whether simple calorie controlled or not, and this is impossible for most people in today's world of plenty.The 5-2 diet does at least enable you to focus your energy on only TWO days and eat normally without worrying on the others. It effectively gives a weekly reduction in calories of around 3600 calories - which will bring your weight down steadily. You can choose which days to fast to fit into your life so you can eat out with friends, go to parties without effort.I have tried it, it has worked effectively for me. My weight is well down, my sugar level is healthy. I shall continue it and eventually move as an experiment to a 6-1 diet which should maintain my weight loss.My only side-effect is constipation! but that has always been a problem in my life, regardless of what I eat.

Boggey79 said on 30 January 2013

My GP told me that 5:2 was a gimmick and I shouldn't waste any time with it...She went as far to say this type of fasting is dangerous. Really?? Frankly I think I shouldn't of wasted my own time making an appointment. Although I was hoping to get my cholesterol checked before starting 5:2 in order to monitor any change. The GP refused to refer me even for a simple cholesterol check! I'm 33 but I have a family history of cardiovascular disease and I'm looking to take pre-emptive measures! Shame the NHS seem also to be taking the same defensive approach. I agree the NHS has a duty to exercise a certain degree of scepticism particularly given the lack of peer-reviewed evidence...But didn't the NHS plough millions into Homoeopathy?

Dothewrongthing said on 29 January 2013

My partner and I decided to start the 5:2 last August. We had succeeded in paying off our mortgage after watching a program on that subject so are easily brainwashed. I've lost a stone in weight and no longer have back pain which had been a problem for me for 3 years a big problem as my work is very labour intensive. I wouldn't call it a diet as I don't have to think about it much on the Monday and Thursday when I consume just 500-600 calories. Please do research as if there are 60 percent adults who are overweight, a really serious problem could be curbed. It's so good to not have a fat gut, after 20 years of trying to eat healthily and slowly putting on the pounds. No side effects noted. No medication involved - just simple maths with the menu ingredients - magic :-)

FF32 said on 29 January 2013

Hi folks,

This diet was mentioned to me by a friend a few weeks ago when I said that I was getting back in the gym in order lose some weight having let myself go over the last couple years.

At first I dismissed the idea of fasting as it went firmly against the way in which I got into great shape around 5 years ago. I followed the "Body for life" framework for diet and exercise which at the time saw me go from 13st 10lbs to 12st in 12 weeks. For those unfamiliar with this diet ut involves eating 5 meals a day with high protein and good carbs for 6 days a week whilst also exercising in the gym. The 7th day was a rest day where you ate what you like. They key thing for me was that although my weight dropped I maintained lean muscle and ended up with a good physique.

I did this diet as a single 27 year old who worked a 9-5 so it was easy for my to be selfish. I trained in the morning at 6:30 before work and ate bland food as food was just fuel. This didn't bother me as I saw results very quickly.

I'm 32 now, just under 6ft and weigh 14st. I've been back in the gym for 4 weeks now but have struggled to be as regimented with my food due to being married and the father of a 2 year old. I can feel a difference in my muscles however I don't feel like I'm losing any body fat.

The long and short of my post is that the health benefits of this diet interest me having lost my father to cancer aged 54. The weight loss prospects are also very interesting to me but I would like to lose fat whilst building/maintaining a muscular physique.

Andrew Ford said on 28 January 2013

I was diagnosed with type 2 diabetes eight years ago and have monitored my morning blood glucose ever since. I am vegetarian and have seen significant improvements from giving up dairy products in May. In August I started IF, having first consulted my GP. He said to modify my medication when I was fasting and I skip the Metformin and Gliclazide on the evenings that I have been fasting. I have dropped my BMI from 26 to 24 since August (lost 14lb) and my blood glucose is about 15% lower. One fasting day I forgot to skip my medication and my blood glucose dropped to 3.3 at midnight, which shows that one does have to take care about the interaction between fasting and medication. Lastly I have heard on the grapevine that my GP has also tried out the IF diet himself.

PeteRichardson said on 25 January 2013

I've been doing 5:2 since August last year and then alternate day since November. y BMI dropped from 26 to 23. This after years of trying and failing to lose weight on the traditional advice. I feel great on my fast days, no side effects at all. The hunger really isn't so bad either. I echo the comments above: the standard advice doesn't work. Fasting does. There is growing evidence to support that fact, as distasteful as some people find it, for whatever reason. The absurd reactions I get from many people when I tell them I'm doing fasting varies from incredulity to fear. Our love of God seems so great that people appear to take the idea of fasting as some kind of threat. It's quite funny really.

Rambunctiousjo said on 25 January 2013

In Islam we were taught that it is good to fast 2 days a week. On Monday and Thursday. The article states that the pattern of IF is unclear,, I think a good place to start is fasting Monday and Thursday.

Ascus said on 25 January 2013

The official advice concerning the 5:2 diet is disappointing and negative. What I would like to see is an attempt to test the validity of the claims by setting up controlled trials.

The recommendation to stick to conventional advice would be sensible if the evidence from controlled experiments was convincing. There is nothing harmful in it but evidence from clinical trials is of low significance and its value is inflated because it is the best straw to cling to.

Why not respond positively and fully test the 5:2 principle instead of dismissing it because such evidence does not yet exist

rogerhyam said on 24 January 2013

I don't smoke, don't drink, am vegetarian, cycle to work each day and do 5k runs. My weight continues rise at about a pound a year as it has done for 20+ years. I've tried just cutting back or watching what I eat and it doesn't work. It makes life miserable because I have to be continuously vigulent about everything I put in my mouth. I can't count up to 2,500 over the course of a day, every day for the rest of my life!

I've been doing the 5:2 for four weeks now. Will weigh myself at the end of the month. I feel good. I feel slimmer. It fits in with the family. If it carries on working I'll keep it up till I get to my target weight and then cut to one day. It is far easier than anything else I have tried to curb my weight gain.

Will it work for everyone? Probably not but I don't care.

The standard advice for weight loss is so effective we have an obesity epidemic. That is pretty good evidence that on a population level it doesn't work. Doing something else that hasn't yet been proved not to work can hardly be knocked.

Peter Gilfedder said on 22 January 2013

I have been on the 5:2 diet for 3 months. I was already slim but have still lost 6 kilos (71kg down to 65kg height 5'9"). However, much more important to me is a reduction in average daily BP from 150/90 or more, to around 130/80. For this reason alone, even if the other claims cannot be substantiated, I intend to continue with the 5:2. I have found it very easy to maintain and feel 'empowered' by it. I prefer to stick to a fixed routine on diet days of 1 poached egg on a small slice of brown toast for breakfast, half a pot of low calorie soup at lunch and fish with plenty of vegetables for dinner. No milk in drinks or alcohol etc on those days. I find the monotony of my fixed diet day menu means I'm simply not interested in food on those days. Peter Gilfedder

CynicalEng said on 20 January 2013

Intermittent Calorie Reduction 2/5 was studied for breast cancer risk reduction by Harvie http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3017674/ "107 premenopausal women aged 30 to 45 years with adult weight gain since the age of 20 exceeding 10kg, and a body mass index (BMI) between 24 and 40 kg/m2" and shown to be effective for fat loss eating 25% of calorie needs for two consecutive days and eating normally for 5 days.

There's a March 2011 review paper at http://onlinelibrary.wiley.com/doi/10.1111/j.1467-789X.2011.00873.x/full by Varady which conculdes "Results reveal similar weight loss and fat mass loss with 3 to 12 weeks' intermittent CR (4–8%, 11–16%, respectively) and daily CR (5–8%, 10–20%, respectively). In contrast, less fat free mass was lost in response to intermittent CR versus daily CR. These findings suggest that these diets are equally as effective in decreasing body weight and fat mass, although intermittent CR may be more effective for the retention of lean mass"

So perhaps the NHS should be encouraging use of these approaches where the tired "healthy eating and exercise" mantra has failed.

penny501 said on 19 January 2013

It works for me and is much easier than dieting every day. # Ricecakes with an egg; # vegetables with a miso broth; # quorn with vegetables make 3 meals on 500 cals -.including the addition of :# 2 fruit snacks and # plenty of water plus herbal teas. I feel great, am more relaxed on fast days and am sleeping much better. Also have much more energy on the other 5 non-fast days which supports the claim that this kickstarts the metabolism.For such a simple diet I find it extraordinary that the above article misses out a key element - the fast days should not be consecutive. It's also easier to exercise on the other five days with enhanced energy levels.As for long term, there's no need Just revert to a couple of fast days for a week now and then if the weight goes up by more than 3lbs. A lot easier than a continuous diet grind, faffing around with points or cals, weights and measures. Sorted!

Paulijohan said on 18 January 2013

I've been doing the 5:2 since the beginning of October last year and have lost 2 inches off my waist and about 10 kg in weight. I fast on Mondays and Wednesdays, but eat very healthily on those days too - boiled eggs and rye toast for breakfast and a small bowl of veg curry for lunch and dinner (with a bit of rice in the evening). I eat normally for the rest of the week and don't avoid any foods (apart from meat and fish as I am veggie). I eat quite healthily, but at the same time I love puddings, cakes, crisps, cheese, wine and beer and indulge in these without overdoing it - and now with losing weight at the same time! On my fast days I do feel hungry, but also sharp and energetic. Overall I feel fitter and more energetic and it's great to be slim again. Only time and in-depth research will tell whether all the possible benefits which have been cited by the Horizon documentary are actually the direct result of this sort of eating pattern. But I think I've found a way to enjoy my guilty pleasures without gaining weight and without, er, feeling guilty.

bringiton said on 18 January 2013

Scepticism is healthy... but flying in the face of the successful experiences of 100s of people who have become healthier and slimmer as a result of 5:2 fast diet is not. If the NHS's weight loss advice was relevant to the way most struggling dieters lived their lives then obesity wouldn't be such a huge and dangerous problem in this country. I for one will take my chances with the 5:2 which is making me feel better than I have in a long time.

uncleringo said on 16 January 2013

This is a very defensive, half-hearted article. There is clearly a lot of evidence that IF reduces many of the levels of things that lead to fatal diseases. There is also overwhelming evidence that people are getting fatter and generally more unhealthy.

Most people these days must clearly know what the government recommended diet is, and yet the situation continues to get worse.

Recommending we stick to the status quo just perpetuates the currrent sleep-walk to an earlier than necessary grave. I applaud the recent investigative work on IF. And it's not a new idea either. We need more people looking for alternatives to the accepted norms of the modern western diet and lifestyle.

I regularly fast, and, like the cyclist here mentions, I've actually seen my athletic performance improve. I ran my fastest half marathon after fasting for 24 hours. I would also like to add that I have not lost any weight (my BMI is around 21), and contrary to feeling sleepy on fast days I generally feel more upbeat and energised.

Obviously it should be pointed out that there may be unknown risks, but it's not good to completely dismiss ideas because the author can't be bothered to do any proper research.

An open mind is a powerful tool. If there's a chance I can live longer and reduce the odds of developing nasty diseases along the way then I'd quite like to give it a go.

saywhatyoulike said on 16 January 2013

You can say what you like, but it works for me.

I started 5:2 fasting on 20/8/12 and so far (16/1/13) I have lost 36lbs in weight and my BMI has gone from 32 to 26. I have lost 4 inches off my waist, my cholesterol and fasting blood sugar readings have returned to a normal range from being in the high risk category for type 2 diabetes and heart disease.

Clearly whoever wrote this article is a sceptic, and maybe 5:2 fasting hasn't been properly researched but it is the sole reason for my health improvements and I am still enjoying my food the rest of the week without being too careful (even over Christmas).

I don't care what nonsense you write on here, the fact is I am proof that it works!

User192980 said on 16 January 2013

keribillen1 said on 16 January 2013

Of course the NHS is not going to promote 5:2 fasting when the science behind it is not yet proven. There are still many necessary studies ongoing. In this situation the NHS cannot be 'blamed' for sticking to its policies and the general advice it gives.

However, apart from the many scientific studies about immoderate intake of alcohol, fat, salt etc. that have been done, the advice of the NHS and other medical professionals is based on conventional wisdom/the accepted norm. This is the least-risk/most-conventional advice to give. However, the accepted norm is not based on scientific research as far as I know, but the centuries of eating habits we've followed. There is no scientific proof that moderate+balanced eating and drinking 3 times per day/seven days per week, with a bit of exercise is the OPTIMUM for health and longevity in humans. This optimum is yet to be found&proven, and unless we perform studies and individual experiments with fasting and other methods then we will never know what the optimum is.

For me, the jury is out and the more experiments there are, the better. I am sure the results will be surprising because I don't accept (without scientific due diligence) that 3 balanced meals per day 7 days per week plus a bit of exercise is the optimum.

Since Nov '12 I am willingly trying the 5:2 regime and I have experience of the side-effects listed above except anxiety and dehydration....it obvious that one should drink more when fasting because there is much water we take when eating food. I am also a regular and vigorous cyclist, and have not noticed a degradation in my athletic performance (I track this obsessively). In fact, I go faster now because I am 6kg lighter!

To summarise, the science is ongoing but I believe we should embrace ideas like 5:2 fasting until they are proven to be detrimental.

craziecreature said on 15 January 2013

Oh come on, why use high fat, high calorie foods as your example of a 500 calorie 'day'?What about fresh fruit, veg and lean meats? I think someone needs to put a little more effort into this, you clearly haven't bothered to do much real reasearch into it. Its your duty to care for our health and I'm actually rather disturbed by the aparent lack of effort put into this.

BGT said on 15 January 2013

This article says "most health professionals" would recommend you stick to conventional advice. So I suppose the key question for 5:2 fans is: what does your GP say?

It's worth noting that the common factor behind the two 'links to the headlines' AND the Horizon program is Michael Mosley. He also did that recent three-part series on Radio 4.

While Mosley did complete a medicine degree (specialism: psychiatry), he's not a qualified nutrionist, he's not an epidemiologist, he's not an expert in public health or in diseases such CVD, stroke or cancer...

And he's no longer independent.

Personally, I'd wait for more evidence before seeing this diet as a long-term solution.

Imnowskinny said on 15 January 2013

What a shoddy piece of journalism. I've been doing 5:2 since August and lost 20lbs and have never felt better. I know some people who have disturbed sleep on a fast day but I sleep like a log.I use my fast days to exercise hard as I feel so full of energy. This is by far the easiest diet I have ever done in my life and I will be continuing forever. I am able to eat whatever I like (within reason) 5 days a week and have to restrict to 500 cals ONLY 2 days per week.Fast days meals always consist of healthy foods (unlike those so foolishly quoted in this article) i.e lean chicken or fish and plenty of vegetables, fruit and yoghurt, black coffee and non milk teas (or with milk from your 500 cals).Also there HAVE been long term studies on humans but they have not been published yet.For real, honest information on 5:2 follow @DrMichaelMosley or a wonderful source of info and guidance, mumsnet.com

Jaktiger said on 15 January 2013

I can't believe the 500 calorie example you quote - call yourself an NHS site!! What happened to fruit & veg & sensible protein options?Your article is biased & not factually correct! You have used none of the current data available. Try asking people who have actually tried the Fast Diet & check the real current data.Including articles like this makes the site look very unprofessional in my opinion when there is good data to show the diet is healthy, sensible & effective.Why trash something you have not fully researched?I have been using a similar type of eating pattern for a long time with good results all round.Try interviewing someone currently using the Fast Diet.

Useful links

NHS Choices links

Develop healthier eating habits and get more active with the 12-week diet and exercise plan

Losing weight: how your GP can help

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A GP talks about visiting your doctor to get help with losing weight. He describes how you'll be assessed and given an individually tailored weight loss plan. Elinor, who had health problems caused by her weight, explains why she asked her GP for help instead of choosing to follow a commercial diet.